Sustainable woodfuel systems: a theory of change for sub-Saharan Africa

The sustainable woodfuel theory of change (SWToC) states that woodfuel can be made truly sustainable in the long run. Sustainable woodfuel implies addressing the negative impacts at every stage of its production, processing, transportation, and use while optimizing socio-economic and cultural benefits and transforming the environmental co-benefits. This includes the health, production and climate change implications of biomass use for fuel. Trees are a renewable resource that tap solar energy, and as long as harvesting does not exceed replenishment, their use can be sustained indefinitely. To address the negative impacts associated with traditional woodfuel use, governments in SSA are developing strategies to increase tree cover and cleaner cooking technologies and practices to meet their Nationally Determined Contributions (NDCs) to mitigate against climate change, and sustainable woodfuel is a critical component in meeting these goals (MoE Republic of Kenya 2020).

Let us not take for granted access to affordable cooking and heating fuel for the poor, both in urban and remote rural locations. In this regard key components of affordable cooking and heating fuel are social, economic as well as technical. In low- and middle-income countries the energy needs of the poor must be included. This is difficult given that the poorest Africans are not an attractive market for for-profit businesses. Currently the firewood and wood used for charcoal is nearly free, and a more sustainable replacement system must address the needs of that segment of the population if it is to succeed. One of the biggest challenges currently is that public-private partnerships struggle in environments where the profit margins, even under optimal design conditions, are essentially zero.

The SWToC connects the four main components of the woodfuel life cycle, including sourcing wood, processing wood into firewood or charcoal, transport and trading, and utilization (figure 1). The SWToC is based on the knowledge that unsustainability and inefficiencies exist in each component, and it offers evidence-based solutions for transformation to sustainable and efficient at each stage. Improving efficiency in one component of the system has implications on another (figure 1). For example, the degree of efficiency in regard to consumption impacts consequent demand by affecting amount of wood required for processing and transportation. Likewise, the degree of efficiency in processing impacts the amount of wood required and area required to grow it. Further, the degree of efficiency in transportation, marketing, and trade affects access to affordable energy, need for processing, and amount of wood required.

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Along the same lines are other concepts such as greening the charcoal value chain to mitigate climate change, and improving local livelihoods through agroforestry combined with improved kilns and stoves to reduce the land area for woodfuel production (Iiyama et al 2014, FAO 2017). This SWToC is in line with the urgent actions recommended in the desk study by UNEP and African Union towards making woodfuel sustainable in Africa (UNEP 2019).

The sustainable woodfuel ToC integrates circular bioenergy economies where by-products at one stage are used as inputs for energy or other processes, closing the resource flow loops while reducing waste and pollution. This way, the woodfuel system positively impacts other biological and social systems.

Woodfuel use in less developed regions of the world is relevant to just about all the Sustainable Development Goals (SDG), and especially to SDG 5 on Gender Equality, SDG7 on Affordable and Clean Energy, SDG13 on Climate Action, and SDG15 on Life on Land. In fact, some of these SDGs call for a reduction or end to the use of woodfuel. Solutions offered under each goal focus on improved technologies and alternative fuels, but we argue that solutions should be rooted in social patterns of use. Household choice is a key factor to understanding why people use certain cooking fuels and cooking appliances (Hollada et al 2017, Gitau et al 2019a), and without an awareness and value assigned to this factor, any solution is likely to fail. Rather than ignoring, or worse, disparaging, woodfuel, people's needs and preferences should be integrated into global research and development, as described by Mendum and Njenga (2018).

At the same time, we highlight a double standard. While woodfuel use by the poor strata of societies is discouraged in SSA, wood is promoted as a modern fuel and a national strategy to reduce greenhouse gases in other continents, especially in the EU. For example, the United Kingdom's Renewable Heat Incentive, introduced in 2014, explicitly includes payment to households using biomass boilers as part of the strategy to reduce the country's greenhouse gas emissions by 80% from 1990 levels by 2050 (OFGEM 2018). A proportion of the charcoal used for barbeque in the global north is sourced from the global South where, for instance, EU in 2019 imported 0.75 million tonnes from the tropics and sub-tropics (Haag et al 2020). This points to the need to rethink woodfuel around the world; the unanswered question is why the double standard.

Unsustainable harvesting of wood for firewood and charcoal contributes to land degradation, deforestation and climate change. With respect to land degradation and deforestation, charcoal is of greater concern than firewood as more biomass is required for conversion to charcoal (Drigo et al 2015, Njenga et al 2017). Further, firewood is mainly gathered from forest residues such as dead wood in natural forests, twigs and branches after timber harvest and poles from plantation forests and trees on-farm (Githiomi et al 2012, Mendum and Njenga 2018, Gitau et al 2019a). It is the case that as the population of SSA increases, forest residues become more scarce and the distance people must walk to gather wood increases. It is thus important to supplement and expand the forest cover in areas where residue collection occurs. In the case of charcoal, producers either clearcut entire stands or selectively harvest preferred species or use tree residues after clearing for agriculture or invasive tree species control (Iiyama et al 2017, Mbaabu et al 2019). Harvesting trees for charcoal is prohibited in protected forests in most if not all countries. If governments would enforce existing regulations, much of the blame for deforestation by woodfuel harvesters would be eliminated.

Technologies exist for scaling sustainable wood production for energy, especially on farms and in landscape restoration (table 1). Growing and managing trees for bioenergy present benefits in multiple ways while integrating a circular bioenergy economy. The trees provide additional ecosystem services, such as provision of shade, fruit and fibre, carbon capture (even if temporary), and soil stabilization (de Leeuw et al 2014). Additional benefits are provided when trees are produced in agroforestry systems where over 20 times more above-and below-ground carbon is found to accumulate than in conventional farming, especially for systems incorporating fertilizer trees (Kaonga and Bayliss-Smith 2009). For optimal benefits in carbon capture, tree replacement and management should ensure a continuous standing biomass.

Traditional producers can transition to more efficient, context-specific technologies for wood processing with concerted efforts in capacity development, integration of local practices and gender considerations, affordable credit facilities, and enabling policy with incentives for compliance.

Traditional earth mound kilns for converting wood to charcoal have low recovery rates, leading to wood wastage and air pollution (FAO 2017). Despite their known negative effects, their use prevails given that they are simple to construct, flexible in size and shape, and mobile. Traditional kiln technology is also low cost and requires only informal labour. Improvements in combustion efficiency during charcoal production reduces both wood input volume and GHG emissions, ultimately contributing to a circular bioenergy economy (table 2, figure 2). For example, improving traditional, inefficient kilns can reduce GHG by 80% for a 100-year Global Warming Potential and reduce the amount of wood required and the area needed to grow it (FAO 2017).

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The introduction and adoption of improved kilns has faced challenges since they require advanced knowledge and higher capital investment. Some of them are stationery, requiring charcoal producers to spend additional resources to move wood (Iiyama et al 2014).

Integral to technology development is the enhancement of producer knowledge. For example, training on wood drying prior to charcoal production, stacking wood in the kiln, kiln ventilation, and generally monitoring the process significantly improved kiln wood to charcoal conversion efficiency from 7% to 22% in the Democratic Republic of Congo (DRC) and 15% to 22% in Kenya (Schure et al 2019, 2021).

To contribute to circularity, the emissions and waste pieces of the carbonization processes can be recovered and converted to other uses. For example, in Brazil, the metallic Rima Container Kiln (RCK) converts 35% of the initial wood to charcoal while producing thermal power (Vilela et al 2014). Work by Bailis et al (2013) in Brazil showed that shift from a hot-tail kiln to metal 'container kilns', which were being tested as a more efficient alternative, reduce greenhouse gas emissions and allow easy capture of pyrolysis gases for production of heat and power. Smoke from traditional kilns can be converted to wood vinegar by condensing captured smoke into liquid. Wood vinegar is used in organic farming to control disease, pests and weeds; for enhancing growth and fruit quality; and for wood preservation and flavouring food (Theapparat et al 2018). Pieces of charcoal too small to burn, called biochar, can serve as a soil amendment (Jeffery et al 2013, Sundberg et al 2020) or are recovered and mixed with a binding agent such as molasses a waste product from sugar factories or soil and compacted into solid units to produce charcoal briquettes (Njenga et al 2014).

Transporting woodfuel is a source of GHG in commercial scale, and the resources saved by using waste materials to make briquettes can be undermined if the end product has to be trucked for long distances. A Life Cycle Assessment (LCA) of briquettes produced using sugarcane waste in Western Kenya showed that the transportation of the briquettes accounted for over 60% of the GHG of the system (Laula et al 2019) because the end users were tea factories located in Central Kenya. As a solution to the high GHG emissions cost of transport in the woodfuel sector, it is recommended to produce wood and other types of biomass for energy near sites of consumption. Coordinating transportation for the charcoal value chain from rural to urban centers should aim at bulking and carrying large quantities to cities while having the vehicles transport another product back to the rural area to minimise the emissions associated with carrying the fuel.

There is a clear need to improve woodfuel cooking systems for human health. In SSA, each year over half a million premature deaths are linked to indoor air pollution caused by cooking with fossil fuels and woodfuel (IEA 2017). Other deaths, though not officially accounted for, may be attributed to under-nutrition resulting from women and children walking long distances to collect firewood (Li et al 2021).

Fine particulate matter (PM_2.5) is a common indicator of the health risk associated with exposure to air pollutants from diverse sources (Lim and Vos 2012). Firewood combustion in the kitchen causes over 100 times higher concentrations of PM_2.5 compared to charcoal (Njenga et al 2017).

More efficient woodfuel stoves can help to lower demand for wood and reduce household air pollution (table 3). Switching to cleaner biomass cook stoves in Asia and Latin America improved health outcomes (Alam et al 2006, Clark et al 2013). Research in the US showed that improving ventilation can also reduce indoor air pollution caused by cooking (Ampollini et al 2019, Farmer et al 2019). International standards for testing fuel use efficiency, total emissions, indoor emissions, and safety of biomass cook stoves are certified by the International Organization for Standardization (ISO) (https://iso.org/standard/66519.html).

Use of firewood is compared to open fire, industrial Jikokoa is compared to Kenya Ceramic Jiko and briquettes (charcoal dust 80% and 20% soil) are compared to charcoal in KCJ

Improving woodfuel cooking systems also contributes to planetary health by reducing both harmful black carbon and GHG emissions. Combustion of woodfuels globally constitutes 25% of atmospheric black carbon, which is a major component of particulate matter and one of the largest contributors to climate change (WHO and Climate and Clean air Coalition 2016). Emissions from woodfuel are 1.0–1.2 Gt CO₂e yr⁻¹ representing 1.9%–2.3% of global emissions (Bailis et al 2015). Successful deployment and utilization of 100 million improved stoves could reduce this by 11% to 17% (Bailis et al 2015). If black carbon was included in carbon markets, at US$11 per tCO2e of avoided emissions, these reductions would be worth over US$1 billion yr⁻¹ (Bailis et al 2015). Further, a shift from traditional stoves to improved stoves could result into a 63% reduction in GHG emissions from charcoal in a 100-year Global Warming Potential (FAO 2017).

Applying a circular bioeconomy perspective in woodfuel cleaner cooking has been demonstrated where, for example, a pyrolytic gasifier cook stove burns dry biomass under controlled oxygen, and the gaseous energy is used for cooking and/or heating while char is produced as a by-product. The harvested char is used as fuel or as biochar for soil improvement with additional benefits of mitigating climate change (Njenga et al 2021a).

Enablers and barriers for adoption of improved biomass stoves have been studied widely, and this new knowledge needs to inform development towards cleaner cooking (Goodwin et al 2015, Brooks et al 2016, Kumar et al 2016, Puzzolo et al 2016, Yip et al 2017). Factors such as convenience of use, heating space, reduced fuel consumption and associated time and cash expenditure, and reduced household air pollution are some of the documented enablers for adoption of improved cook stoves (Agbokey et al 2019, Gitau et al 2019a). Functional characteristics such as need to cut firewood into small pieces, continued management of fuel, need to refill fuel canister and relight the stove in the middle of cooking, size of stove, household size, type of food and cost of stove and repairs are some of the key identified barriers inhibiting adoption of improved stoves (Hollada et al 2017, Agbokey et al 2019, Gitau et al 2019a). Compatibility with local cooking culture summarises most of these barriers, though the knowledge possessed by women as main cooks often has been overlooked.

Gender disparities characterise both household and commercial sectors of the woodfuel economy in sub-Saharan Africa. With few exceptions, the labour burden for household firewood collection falls entirely on women, who generally collect and transport bundles of wood on foot. Unfortunately, the literature on biomass energy, renewable energy use and technology does not include a comprehensive analysis of important issues such as the economic value of time spent currently on inefficient woodfuel activities or the gendered distribution of household woodfuel use versus even the most low-levels of commercial activities. A comprehensive survey of the most recent literature on renewable energy in Africa, for example, shows a focus on technology and non-wood biomass options (Afrane et al 2022). Even studies of energy use among the poor in Africa focuses on charcoal and biogas without considering the entire woodfuel system (Karakezi 2002).

At the household level, the barriers to studying the portion of the woodfuel system used by rural and urban populations, including refugees, include lack of funding for study of the social—as opposed to the technical—factors that influence the use and innovation around woodfuel use. Until very recently, donor organizations and governments have focused on transitioning to 'modern' energy sources, including fossil fuels like LPG, or renewables like solar energy for electricity generation. Neither of these options addresses the majority of household users in Africa, namely poor and middle-income women. There exists a rich literature on informal work on the continent, again, not specific to woodfuel use but which would provide a useful structure for a detailed study of this kind (Khavul et al 2009, Lindell 2010, Jackson 2012, Grant 2013).

One additional issue that is important to understanding woodfuel use is the legal situation regarding refugees who use woodfuels harvested from local resources, often in arid areas. The wars and political instability in South Sudan, the Democratic Republic of the Congo and Somalia have resulted in substantial refugee populations in East Africa, for example. The civil war and continuing conflict in Ethiopia has exacerbated the large numbers of individuals on the move. With the exception of Uganda, which has a unique and inclusive approach to refugee integration, refugees are not allowed to work or travel freely outside of UNHCR camps set up for their accommodation. This means that the economic potential of refugees is difficult to measure empirically and the environmental and human damage done by mismanaged or unmanaged woodfuel collection and use systems has a substantial unmeasured impact on people, animals, and the larger environment. The same situation in also true in other parts of the continent with similar results.

In the commercial sector, women tend to be involved in the low-income segments of the woodfuel market such as in production and retailing of charcoal. Their male counterparts dominate segments further down the supply chain, such as transportation and wholesale trade, where profit margins are higher (Ihalainen et al 2020). This gender disparity is associated with access and control over productive resources and income, social and political capital, and gender roles and responsibilities (Ihalainen et al 2020).

There is need for gender equality enhancement in benefit sharing, which could be achieved through gender analysis and gender integration along the value chains for enhanced socio-economic sustainability. Wood production and processing technologies are often tied to the availability of transport, which is governed by who controls the modes of transport. Transport, marketing, and trade are highly gendered.